Fish-farming solid feed and process for producing same

ABSTRACT

A fish-farming solid feed containing stabilized vitamin C, wherein at least 50% by mass of stabilized vitamin C, based on the total weight thereof contained in the solid feed, is present in a surface layer portion of the solid feed, spanning from the surface to a 1 mm depth; or the content of stabilized vitamin C in a surface layer portion spanning from the surface to a 1 mm depth of the solid feed is at least 50 ppm by mass. The fish-farming solid feed can be produced by a process wherein a fish-farming feed material is kneaded and shaped into a shaped product; the shaped product is dried; and then, the dried shaped product is contacted with stabilized vitamin C having been dissolved, emulsified or dispersed in a liquid such as vegetable or animal oil, preferably fish oil.

CROSS-REFERENCE TO RELATED APPLICATION

This application is an application filed under 35 U.S.C. § 111(a)claiming benefit pursuant to 35 U.S.C. § 119(e)(1) of the filing date ofProvisional Application 60/374,814 filed Apr. 24, 2002, pursuant to 35U.S.C. § 111(b).

TECHNICAL FIELD

This invention relates to a fish-farming solid feed containing anascorbic acid derivative which exhibits an ascorbic acid activity and isstable, especially stable with time in the feed; and a process forproducing the fish-farming solid feed.

BACKGROUND ART

It is well known that deficiency or shortage of L-ascorbic acid incultured fishes causes scurvy which occasionally causes death. Forexample, a plurality of abnormal fishes signed with scoliosis developedin many rainbow trout fishfarms in 1962. It was proved that thesesymptoms are caused by deficiency of L-ascorbic acid (Japan FisheriesSociety, vol. 31, p 818-826). Deformed juvenile rainbow trout, redsalmons and chum salmons were reported as caused by deficiency ofascorbic acid, in Annual Meeting of Japan Fisheries Society in 1967.Further, as examples of ascorbic acid deficiencies, there can bementioned anorexia, slight exophthalmus, hemorrhage at a fin bottom,damage of gill cover and cervical damage in ayu sweet fish; feedingreduction, growth stop, scoliosis, abnormal pigmentation and highmortality rate in juvenile Japanese amberjack; and anorexia, growthreduction, fin hemorrhage and head hemorrhage in Japanese eel. Due tostress caused during culturing, a larger quantity of ascorbic acid isrequired for cultured fishes such as rainbow trout, red salmon, chumsalmon, ayu sweet fish, cherry salmon, greater amberjack, Japaneseamberjack, sea bream, common carp and Japanese eel, than the quantityrequired for wild fishes.

Thus ascorbic acid is an essential supplement for feed. In practice,vitamins including ascorbic acid are incorporated in a feed for juvenilefishes. However, ascorbic acid is an unstable water-soluble vitamin, andis easily decomposed within the feed. Ascorbic acid is extremelyunstable especially in fish meal as a protein source, and thus, it'svitamin C titer is greatly reduced by decomposition in a feedpredominantly comprised of fish meal, such as feed for rainbow trout.

It is also known that, when a fish meal having ascorbic acidincorporated therein is kneaded and extruded under high-pressure andhigh-temperature conditions by an extruder in the course of productionof a fish-farming feed, ascorbic acid is readily decomposed (forexample, see Japanese Unexamined Patent Publication No. H11-056256). Inthis patent publication, a technique is disclosed wherein an emulsion ofwater-soluble vitamins is applied to fish-farming feed pellets shapedfrom fish meal by an extruder. This technique is considered to avoid orminimize decomposition of water-soluble vitamins caused during kneadingand extrusion by an extruder.

To remedy the problem of decomposition of vitamin C, an attempt ofincorporating vitamin C of a stabilized form, such as salts ofL-ascorbate 2-phosphate, in a fish-farming solid feed has been proposed,for example, in U.S. Pat. No. 2,943,785. However, the present inventorshave found that, when the fish-farming solid feed is of a globular orcolumnar shape having a large diameter, or a large amount of vegetableoil and/or animal oil as a nutrient is incorporated in the fish-farmingsolid feed, vitamin C tends to be decomposed to some extent even if itis of a stabilized form. The degradation of the vitamin C-incorporatedfish-farming solid feed proceeds also during storage.

DISCLOSURE OF THE INVENTION

In view of the foregoing, a primary object of the present invention isto provide a stable fish-farming solid feed having incorporated thereinstabilized vitamin C exhibiting high vitamin C titer which is reducedonly to a minimum extent during the course of production and storage.Especially even when the stabilized vitamin C-incorporated fish-farmingsolid feed has a large size and/or has incorporated therein a largeamount of vegetable oil and/or animal oil, the fish-farming solid feedexhibits a high vitamin C titer which is reduced only to a minor extentduring the course of production and storage.

The present inventors made extensive research and found that partialdecomposition of stabilized vitamin C including a salt of L-ascorbate2-phosphate, as observed when a fish-farming solid feed containing thestabilized vitamin C is of a large size and/or the solid feed contains alarge amount of vegetable oil and/or animal oil, occurs predominantly atthe step of drying pellets as shaped at a kneading and shaping stepusing an extruder. Therefore, the inventors attempted to producefish-farming feed pellets by a process wherein a fish-farming feedmaterial is kneaded and shaped into pellets without incorporation ofstabilized vitamin C, and then, after the pellets are dried, stabilizedvitamin C is applied to the dried pellets, and found the substantialpart of stabilized vitamin C, thus-lately applied, can be retainedwithout any significant deterioration. That is, the thus-appliedstabilized vitamin C keeps its high vitamin C titer and exhibits highstability with time in the feed pellets. Based on these findings, thepresent invention has been completed.

Thus, in accordance with the present invention, there are provided thefollowing fish-farming solid feeds and processes for producing thefish-farming solid feeds.

Fish-Farming Solid Feed

(1) A fish-farming solid feed containing stabilized vitamin C,characterized in that at least 50% by mass of stabilized vitamin C,based on the total weight thereof contained in the solid feed, ispresent in a surface layer portion of the solid feed, spanning from thesurface to a 1 mm depth.

(2) A fish-farming solid feed containing stabilized vitamin C,characterized in that the content of stabilized vitamin C in a surfacelayer portion spanning from the surface to a 1 mm depth of the solidfeed is at least 50 ppm by mass.

(3) The fish-farming solid feed as described in above (1) or (2),wherein the content of stabilized vitamin C in a surface layer portionspanning from the surface to a 1 mm depth of the solid feed is at least100 ppm by mass.

(4) The fish-farming solid feed as described in any one of above (1) to(3), wherein the total content of stabilized vitamin C in the solid feedis in the range of 25 ppm to 5,000 ppm by mass.

(5) The fish-farming solid feed as described in any one of above (1) to(4), which further contains at least one kind of oil selected from thegroup consisting of vegetable oils and animal oils.

(6) The fish-farming solid feed as described in any one of above (1) to(4), which further contains 10% to 40% by mass, based on the mass of thesolid feed, of a fish oil.

(7) The fish-farming solid feed as described in any one of above (1) to(6), wherein the solid feed has a water content of not larger than 10%by mass.

(8) The fish-farming solid feed as described in any one of above (1) to(7), which has a globular or columnar shape and has a diameter of atleast 11 mm.

(9) The fish-farming solid feed as described in any one of above (1) to(8), wherein the stabilized vitamin C is a salt of L-ascorbate2-phosphate.

(10) The fish-farming solid feed as described in claim 9, wherein thesalt of L-ascorbate 2-phosphate is at least one salt selected from thegroup consisting of magnesium, calcium, sodium and potassium salts ofL-ascorbate 2-phosphate, and mixed metal salts thereof.

(11) The fish-farming solid feed as described in any one of above (1) to(10), which is used for feeding a fish or other aquatic animal selectedfrom rainbow trout (Oncorhynchus mykiss), red salmon (sockeye salmon,Oncorhynchus nerka), chum salmon (keta salmon, Oncorhynchus keta), ayusweet fish (plecoglossus altivelis), Biwa trout, cherry salmon (masusalmon, plecoglossus masou), tuna (Thunnini), white trevally(Pseudocaranxdentex), greater amberjack (Serioladumerili), Japaneseamberjack (Seriola quinqueradiata), sea bream (porgy, Sparidac),Japanese seabass (Lateolabrax japonicus), tiger puffer (ocellate puffer,Takifugu rubripes), puffer (Teraodontidac), bastard halibut(paralichthys olivaceus), goldfish, common carp (Cyprinus carpio),Japanese eel (Anguilla japonica), kuruma prawn (Japanese shrimp, Penaeusjaponicus) and black tiger prawn (giant tiger prawn, Penaeus monodon).

Process for Producing the Fish-Farming Solid Feed

(12) A process for producing a fish-farming solid feed as described inany one of above (1) to (11), characterized in that a fish farming feedmaterial is kneaded and shaped into a shaped product; the shaped productis dried; and then, the dried shaped product is contacted withstabilized vitamin C having been dissolved, emulsified or dispersed in aliquid.

(13) The process for producing a fish-farming solid as described inabove (12), wherein the kneading of the fish-farming feed material iscarried out by a heated kneader.

(14) The process for producing a fish-farming solid feed as described inabove (12) or (13), wherein the drying of the shaped product is carriedout to an extent such that the water content in the shaped product isreduced to 10% by mass or lower.

(15) The process for producing a fish-farming solid feed as described inany one of above (12) to (14), wherein the drying of the shaped productis carried out at a temperature of at least 110° C.

(16) The process for producing a fish-farming solid feed as described inany one of above (12) to (15), wherein the drying of the shaped productis carried out for at least two hours.

(17) The process for producing a fish-farming solid feed as described inany one of above (12) to (16), wherein the stabilized vitamin C isparticles having an average particle diameter in the range of 5 μm to300 μm.

(18) The process for producing a fish-farming solid feed as described inany one of above (12) to (17), wherein the liquid in which stabilizedvitamin C has been dispersed comprises at least one kind of oil selectedfrom the group consisting of vegetable oils and animal oils.

(19) The process for producing a fish-farming solid feed as described inany one of above (12) to (17), wherein the liquid in which stabilizedvitamin C has been dispersed comprises a fish oil.

(20) The process for producing a fish-farming solid feed as described inany one of above (12) to (19), wherein, after the dried shaped productis contacted with stabilized vitamin C having been dissolved, emulsifiedor dispersed in the liquid, the resulting shaped product having theliquid deposited thereon is dried.

(21) The process for producing a fish-farming solid feed as described inabove (20), wherein the drying of the product having the liquiddeposited thereon is carried out at a temperature of not higher than 90°C.

(22) The process for producing a fish-farming solid feed as described inany one of above (12) to (21), wherein the as-produced fish-farmingsolid feed contains, as measured immediately after the productionthereof, at least 60% by mass of stabilized vitamin C based on theamount of stabilized vitamin C incorporated in the shaped product whenthe shaped product is contacted with the stabilized vitamin C-containingliquid.

BEST MODE FOR CARRYING OUT THE INVENTION

The kind of stabilized vitamin C used in the present invention is notparticularly limited provided that it exhibits higher stability withtime in a fish-farming feed than that of natural vitamin C and it iscapable of being converted to vitamin C within a living body. Thestabilized vitamin C includes, for example, salts of L-ascorbate2-phosphate, and L-ascorbate 2-glucoside. As preferable examples of thestabilized vitamin C, there can be mentioned magnesium, calcium, sodiumand potassium salts of L-ascorbate 2-phosphate, and mixed metal saltsthereof such as, for example, a sodium/calcium mixed salt of L-ascorbate2-phosphate. These stabilized vitamin C may be used either alone or as acombination of at least two thereof.

If non-stabilized vitamin C, for example, natural vitamin C or calciumL-ascorbate is used, a resulting fish-farming solid feed exhibitsremarkable degradation due to decomposition of non-stabilized vitamin Coccurring during storage as well as at a drying step in the productionprocess.

The stabilized vitamin C-containing fish-farming solid feed of thepresent invention is characterized in that at least 50% by mass ofstabilized vitamin C, based on the total weight thereof contained in thesolid feed, is present in a surface layer portion of the solid feed,spanning from the surface to a 1 mm depth; or, in that the content ofstabilized vitamin C in a surface layer portion spanning from thesurface to a 1 mm depth of the solid feed is at least 50 ppm by mass.

The amount of stabilized vitamin C present in a surface layer portion ofthe solid feed, spanning from the surface to a 1 mm depth of the soldfeed is preferably at least 60% by mass, more preferably at least 65% bymass, based on the total weight thereof contained in the solid feed. Theupper limit thereof is not particularly limited, but it is usually about95% by mass.

The content of stabilized vitamin C in a surface layer portion spanningfrom the surface to 1 mm depth of the solid feed is preferably at least100 ppm by mass, more preferably at least 200 ppm by mass and especiallypreferably at least 250 ppm by mass. The upper limit of the content inthe surface layer portion is not particularly limited, but its upperlimit is usually about 1.5% by mass.

The total content of stabilized vitamin C in the solid feed is usuallyin the range of 25 ppm to 5,000 ppm by mass, preferably 100 ppm to 4,000ppm by mass and more preferably 100 ppm to 2,000 ppm by mass.

The fish-farming solid feed of the present invention containingstabilized vitamin C in a large proportion or content in a surface layerportion thereof is prepared preferably by a process wherein afish-farming feed material is kneaded and shaped into a shaped product;the shaped product is dried; and then, the dried shaped product iscontacted with stabilized vitamin C having been dissolved, emulsified ordispersed in a liquid. If desired, a some amount of vitamin C can beincorporated in the starting fish-farming feed material additionallybefore it is kneaded and shaped, in addition to the lately appliedamount of stabilized vitamin C.

The kneading and shaping of the fish-farming feed material is carriedout usually by a heated kneader. The kneader used is not particularlylimited and includes, for example, an extruder.

The manner in which the dried shaped product is contacted withstabilized vitamin C having been dissolved, emulsified or dispersed in aliquid is not particularly limited, provided that a desired amount ofstabilized vitamin C is incorporated in a desirably distributed fashionin the dried shaped product. Any particular limitation is not imposed tothe kind of liquid used, but a liquid containing water is notpreferable. If a liquid containing water is used, drying is a gainrequired and the drying may cause decomposition of applied stabilizedvitamin C. It is preferable in view of stability that stabilized vitaminC is applied as an oily slurry which is a dispersion in at least one oilselected from vegetable oils and animal oils. More preferably,stabilized vitamin C is dispersed in fish oil. When an oily slurry isused, stabilized vitamin C has reduced chance of contacting with water,and its decomposition due to hydrolysis can be minimized.

The stabilized vitamin C used is preferably particles having an averageparticle diameter in the range of 5 μm to 300 μm. The average particlediameter as used herein means a number average particle diameter whichis measured by a laser diffraction particle size distribution analyzer(“Micro-track MK-II” available from Nikkisou K.K.). If the particlediameter is too large, the stabilized vitamin C is difficult to beuniformly deposited on the surface of solid feed. In contrast, if theparticle diameter is too small, the stabilized vitamin C is difficult tohandle.

The liquid in which stabilized vitamin C is dispersed includes vegetableoil and animal oil, which are conventionally added in a fish-farmingsolid feed. As specific examples of the vegetable oil and animal oil forfish-farming solid feed, there can be mentioned soybean oil and otherbean oils, rape-seed oil, corn oil, sesame oil, cotton-seed oil,safflower oil, sunflower oil, peanut oil, rice germ oil, wheat germ oil,camellia (Japanese rose, tsubaki) oil, palm oil, olive oil, jojoba oil,macadamia nut oil, avocado oil, caster-oil, beafsteak plant oil,eucalyptus oil, evening primrose oil, turtle oil, mink oil, lard, beeftallow and fish oil. Of these, fish oil is preferable. Cod oil andsardine oil are especially preferable. These vegetable oils and animaloils may be used either alone or as a mixture of at least two thereof.

If stabilized vitamin C is applied as an emulsion, an emulsifier is usedfor the preparation thereof. The emulsifier used includes, for example,sorbitan fatty acid esters, glycerin fatty acid esters, organic acidmonoglycerides, propylene glycol fatty acid esters, diglycerides,sucrose fatty acid esters, polyglycerin fatty acid esters, recithin,silicone surfactants and alkylene oxide-added surfactants. As specificexamples of the emulsifier, there can be mentioned sorbitan monooleate,sorbitan distearate, polyoxyethylene (6 mols) sorbitan monostearate,glycerin monostearate, glycerin monolinolate, an esterified product ofcitric acid with glycerin monooleate, propylene glycol monostearate,glycerindioleate, glycerindilinolate, diglyceride obtained by esterinterchange reaction of rape-seed oil with glycerin, diglycerideobtained by ester interchange reaction of safflower oil with glycerin,diglycerin distearate, diglycerin tristearate, hexaglycerin trioleate,hexaglycerin pentastearate, tetraglycerin condensed ricinolate,polyglycerin condensed ricinoleic acid ester, sucrose tri-, tetra- orpenta-stearate, polyoxyethylene (5 mols) cetyl ether, polyoxyethylene (3mols) nonylphenyl ether, polyoxyethylene (6 mols) stearyl ether,polyoxyethylene (5 mols) hardened castor-oil, polyoxyethylene (15 mols)hardened castor-oil, polyoxyethylene (20 mols) sorbitol tetraoleate,lecithin (e.g., Lecithin DX, Baycis LP-20, available from The NisshinOil Mills, Ltd.), dimethylsiloxane-methyl(polyoxyethylene (5mols)-added) siloxane copolymer, sucrose fatty acid ester, polyglycerinfatty acid ester, lysolecithin, saponin, glycolipid, protein, proteindecomposition products (other than gelatin), succrose stearic acidmonoester, hexaglycerin oleic acid monoester, decaglycerin stearic acidmonoester, enzyme-decomposed lecithin (e.g., Baycis LG-10K, BaycisLP-20E, available from The Nisshin Oil Mills, Ltd.), quillaiae saponin,soybean protein decomposition product, casein sodium,dimethylsiloxane-methyl(polyoxyethylene (60 mols)-added) siloxanecopolymer, polyoxyethylene (25 mols) hardened castor-oil andpolyoxyethylene (80 mols) hardened castor-oil.

The contact of a dried shaped product of a fish-farming feed materialwith stabilized vitamin C is conducted in a manner such that usually 25to 5,000 ppm by mass, preferably 100 to 4,000 ppm by mass and morepreferably 100 to 3,000 ppm by mass of stabilized vitamin C, based onthe weight of the dried shaped product, is incorporated in the driedshaped product. As examples of the procedure for incorporating thedesired amount of stabilized vitamin C in the dried shaped product,there can be mentioned a procedure wherein the dried shaped product isdipped in a liquid having stabilized vitamin C dissolved, emulsified ordispersed therein; a procedure wherein the dried shaped product iscoated with a liquid having stabilized vitamin C dissolved, emulsifiedor dispersed therein; and a procedure wherein a liquid having stabilizedvitamin C dissolved, emulsified or dispersed therein is sprayed oratomized on the dried shaped product.

It is essential that a surface layer portion of the solid feed, spanningfrom the surface to a 1 mm depth, contains either at least 50% by massof stabilized vitamin C, based on the total weight thereof contained inthe solid feed, or, in a content of at least 50 ppm by mass. However,the bond strength of stabilized vitamin C to the solid feed is notparticularly limited, provided that a predominant part of the depositedstabilized vitamin C is not separated during transportation from aproducing district to a consumption district. An acceptable bondingstrength can be obtained by the above-mentioned dipping, coating orspraying procedure of applying a stabilized vitamin C-containing liquidto the solid feed.

The fish-farming solid feed of the present invention preferably containsat least 10% by weight, more preferably 10% to 40% by mass andespecially preferably 20% to 30% by mass of vegetable oil and/or animaloil.

To enhance the rate of absorption of vegetable oil and/or animal oilhaving dispersed therein stabilized vitamin C, the shaped product offish-farming feed material is preferably dried prior to application ofthe vegetable oil and/or animal oil to an extent such that the watercontent in the shaped product is reduced to 10% by mass or lower, morepreferably 5% by mass or lower. If the water content in the shapedproduct is high, the rate of absorption of oil is low, and theefficiency of deposition of stabilized vitamin C is reduced. But, toolow water content, e.g., of about 1% by mass or lower, is not preferablebecause such a low water content is difficult to attain and asubstantially long drying time is required with the result of partialdecomposition of the active ingredient.

The drying of the shaped product as carried out after kneading andshaping of a fish farming feed material can be carried out usually at atemperature of at least 110° C., preferably in the range of 110° C. to130° C. for at least 2 hours, preferably in the range of 2 to 4 hours.

After the dried shaped product is contacted with stabilized vitamin Chaving been dissolved, emulsified or dispersed in a liquid, the shapedproduct having the liquid deposited thereon is preferably further dried.This further drying is preferably carried out at a temperature of nothigher than 90° C., especially preferably in the range of 55° C. to 75°C., so as to avoid decomposition of stabilized vitamin C.

Stabilized vitamin C is retained at a high ratio in the fish-farmingsolid feed of the present invention. That is, the solid feed contains atleast 60%, preferably at least 80% and more preferably at least 90%, ofstabilized vitamin C as measured immediately after the productionthereof, based on the amount of stabilized vitamin C incorporated in thesolid feed.

The shape of the fish-farming solid feed is not particularly limited,and includes, for example, column-shape, globe-shape and squarepillar-shape. Especially a column-shaped solid feed called as dry pelletmade by using an extruder is widely used. The fish-farming solid feedpreferably has a diameter of at least 11 mm, more preferably at least 12mm and especially preferably at least 15 mm. The upper limit of thediameter is not particularly limited, but is preferably 30 mm, morepreferably 25 mm.

The ingredients contained in the fish-farming solid feed of the presentinvention, other than stabilized vitamin C, are not particularlylimited, and can be those which are used in conventional fish-farmingsolid feeds, such as cereals, pulses, taros and potatoes, oil cakemeals, brans, secondary products, animal feeds, vitamins, minerals, andcompositions comprised of raw materials.

As specific examples of the cereals, pulses, taros and potatoes, therecan be mentioned corn, milo (grain sorghum), wheat, barley, rye, oats,wheat flour, unhulled rice, millet seed, soybean, soybean flour andcassaba.

As specific examples of the oil cake meals, there can be mentionedsoybean oil meal, skin-removed soybean oil meal, cotton seed oil meal,rape-seed oil meal, peanut oil meal, linseed oil meal, sesame oil, palmoil meal, safflower oil, sunflower oil, palm nut oil meal and kapok oilmeal.

As specific examples of the brans, there can be mentioned rice bran,white sake rice bran, defatted rice bran, wheat bran and barley-mixedbran.

As specific examples of the secondary products, there can be mentionedcorn gluten feed, corn gluten meal, starch lees, molasses lees, soystrained lees, beer strained lees, beet pulp, bagasse, bean-curdsrefuse, malt root and orange juice strained lees.

As specific examples of the animal feed, there can be mentioned fishmeal, white fish meal, fish solubles, fish solubles-adsorbed feed, meatmeal, meat-and-bone meal, blood meal, feather meal, crab meal, shrimpmeal, chrysalis oil meal, skim milk powder, dry whey and animal fat.

As specific examples of the minerals, there can be mentioned sodiumchloride, potassium chloride, ferrous citrate, aluminum hydroxide,magnesium carbonate, calcium lactate, magnesium sulfate, sodiumdihydrogenphosphate, ferric citrate, ferrous sulfate, potassium iodideand potassium iodate.

Further, the following ingredients can be mentioned. Vegetable oils andfats such as soybean oil, rape-seed oil, corn oil and sesame oil; beeryeast, torula yeast, alfalfa meal, orange-peel, corn-tangle meal, tangle(kelp) meal, wakame sea-mustard meal, freshwater Chlorella, marineChlorella, cellulose powder and carboxy-cellulose, and vitamin-mixedfeeds thereof.

The fish-farming solid feed of the present invention is given tofreshwater fishes, marine fishes and other aquatic animals such ascrustaceans. As specific examples of the freshwater fishes and marinefishes, there can be mentioned rainbow trout (Oncorhynchus mykiss), redsalmon (sockeye salmon, Oncorhynchus nerka), chum salmon (keta salmon,Oncorhynchus keta), ayu sweet fish (plecoglossus altivelis), Biwa trout,cherry salmon (masu salmon, plecoglossus masou), tuna (Thunnini), whitetrevally (Pseudocaranx dentex), greater amberjack (Seriola dumerili),Japanese amberjack (Seriola quinqueradiata), sea bream (porgy,Sparidac), Japanese seabass (Lateolabrax japonicus), tiger puffer(ocellate puffer, Takifugu rubripes), puffer (Teraodontidac), bastardhalibut (paralichthys olivaceus), goldfish, common carp (Cyprinuscarpio) and Japanese eel (Anguilla japonica). As specific examples ofthe crustaceans, there can be mentioned crustaceans, kuruma prawn(Japanese shrimp, Penaeus japonicus), black tiger prawn (giant tigerprawn, Penaeus monodon), river prawn (Macrobrachium spp.), swimming crab(horse crab, Portunus trituberculatus), Japanese spiny lobster(Panulirus japonicus), Japanese taisho prawn, western white shrimp,Chinese prawn (Penaeus chinensis), greasyback shrimp (Metapenaeusensis), Japanese fan lobster (ahovel-nosed lobster, slipper lobster,Ibacus ciliatus), Japanese lobster (Metanephrops japonicus), Sakurashrimp (Sergialucens), ediblemantis shrimp (Oratosquillaoratoria),prawn, Japanese crayfish (Cambroides japonicus), lobster (Homarusamericanus), tanner crab (Chionoecetes opilio), Alaskan king crab(Paralithodes camtschaticus) and helmet crab (Pagurus spp.). Thefish-farming solid feed is especially suitable for typical culturedfishes and crustaceans such as rainbow trout (Oncorhynchus mykiss), redsalmon (sockeye salmon, Oncorhynchus nerka), chum salmon (keta salmon,Oncorhynchus keta), ayu sweet fish (plecoglossus altivelis), Biwa trout,cherry salmon (masu salmon, plecoglossus masou), tuna (Thunnini), whitetrevally (Pseudocaranx dentex), greater amberjack (Seriola dumerili),Japanese amberjack (Seriola quinqueradiata), sea bream (porgy,Sparidac), Japanese seabass (Lateolabrax japonicus), tiger puffer(ocellate puffer, Takifugu rubripes), puffer (Teraodontidac), bastardhalibut (paralichthys olivaceus), goldfish, common carp (Cyprinuscarpio), Japanese eel (Anguilla japonica), kuruma prawn (Japaneseshrimp, Penaeus japonicus) and black tiger prawn (giant tiger prawn,Penaeus monodon).

EXAMPLES

The invention will be described specifically by the following examplesthat by no means limit the scope of the invention. % in the examples isby mass unless otherwise specified.

In the working examples, the content of a vitamin C derivative(magnesium salt, sodium salt or calcium salt of L-ascorbate 2-phosphate,or calcium salt of L-ascorbic acid) in a solid feed was determined asfollows.

A solid feed containing a vitamin C derivative was thoroughly pulverizedand placed in a mixed liquid (an aqueous 1% metaphosphoric acidsolution/chloroform=1/1 [v/v]). The mixture was shaken to extract thevitamin C derivative. An aqueous phase containing the extracted vitaminC derivative was analyzed by high performance liquid chromatography(HPLC) under the following conditions.

-   -   Column: “SHODEX™” J411 available from Showa Denko K.K.    -   Eluting solution: Mixed liquid of acetonitrile:        0.05M-KH₂PO₄=60:40 (v/v)    -   Temperature: 40° C.    -   Flow rate: 1.0 ml/min.    -   Detection: UV with wavelength of 257 nm

Example 1

Fish meal, wheat flour, soybean cake meal and fish oil were mixedtogether at a mass ratio of 60%, 15%, 5% and 20%, respectively, and, toenhance knead ability, water in an amount equal to the fish oil wasadded to the mixture. Then the mixture was kneaded thoroughly andextruded by an extruder into a columnar extrudate having a diameter ofabout 14 mm. The columnar extrudate was pelletized and dried at 120° C.for 3 hours until the water content became below 5% to give columnarfeed pellets.

Magnesium salt of L-ascorbate 2-phosphate (“Phospitan™ C” available fromShowa Denko K.K.; average particle diameter: 15 μm) (hereinafterabbreviated to “APM” when appropriate) was dispersed in fish oil toprepare an oily APM suspension having a concentration of 5,000 ppm bymass. The feed pellets were immersed in the oily APM suspension. Afterthe immersion, the weight of feed pellets was increased by 5%. The 5%increase indicated that the amount of APM taken into the pellets was 250ppm by mass. APM was extracted from the pellets and its amount wasmeasured. The measured value was 234 ppm by mass.

The APM-containing feed pellets were stored at 40° C. and, when one day,3 days, 5 days and 10 days elapsed, APM was extracted and its amount wasmeasured. The measured values (APM content in ppm) and retention (%) ofAPM content are shown in Table 1. TABLE 1 Retention of APM contentNumber of days elapsed 1 3 5 10 Content of APM (ppm) 227 225 225 222 APMRetention (%) 97 96 96 95

Example 2

A surface layer portion having a thickness of about 1 mm was shaven fromthe APM-containing feed pellets as made and before storage in Example 1.The surface layer portion was 0.53 g and the remaining core portion was0.90 g. APM content in each portion was measured. The surface layerportion and the core portion contained APM in amounts of 510 ppm by massand 75 ppm by mass, respectively.

Example 3

Solid feed pellets were made by the same procedures as described inExample 1 except that each of sodium salt of L-ascorbate 2-phosphate(hereinafter abbreviated to “APS”) and calcium salt of L-ascorbate2-phosphate (hereinafter abbreviated to “APC”) was separately usedinstead of APM. APS used was prepared by the process described inJapanese Unexamined Patent Publication No. H09-077784, and waspulverized into an average particle diameter of 15 μm. APC used wasprepared by the process described in Japanese Unexamined PatentPublication No. H06-184173, and was pulverized into an average particlediameter of 15 μm.

The APS- or APC-containing feed pellets were tested for their APS or APCcontent. The APS content was 230 ppm by mass and the APC content was 225ppm by mass. These feed pellets were further tested for their APS- orAPC-content retention (%) by the same methods as described in Example 1.The results are shown in Table 2 and Table 3, respectively. TABLE 2Retention of APS content Number of days elapsed 1 3 5 10 Content of APS(ppm) 225 224 222 220 APS Retention (%) 98 97 97 96

TABLE 3 Retention of APC content Number of days elapsed 1 3 5 10 Contentof APC (ppm) 220 219 215 215 APC Retention (%) 98 97 96 96

EXAMPLE 4

An APM-containing aqueous phase was prepared by dissolving 0.5 g of thesame APM as used in Example 1, in 49.5 g of water. An oily phase wasprepared by dissolving 5 g of hexaglycerin condensed ricinoleic acidester (“Poem™” PR-300, available from Riken Vitamin K.K., HLB: 1.7) in50 g of soybean oil at 80° C. While the aqueous phase was graduallyadded into the oily phase, the two phases were mixed together by ahomomixer at 60° C. and 6,000 rpm for 20 minutes to give anAPM-containing emulsion.

A feed material mixture was kneaded, extruded and dried by the sameprocedures as described in Example 1 to give feed pellets. 0.5 g of theabove-mentioned APM-containing emulsion was sprayed on 10 g of the feedpellets, and then the resulting feed pellets were air-dried. The contentof APM in the as-made feed pellets was 228 ppm by mass.

Example 5

An aqueous APM solution was prepared by dissolving 0.5 g of the same APMas used in Example 1 in 99.5 g of water. A feed material mixture waskneaded, extruded and dried by the same procedures as described inExample 1 to give feed pellets. 0.5 g of the above-mentioned aqueous APMsolution was sprayed on 10 g of the feed pellets, and then the resultingfeed pellets were air-dried. The content of APM in the as-made feedpellets was 230 ppm by mass.

Example 6

The same APM as used in Example 1 was dispersed in fish oil to preparean oily APM suspension having a concentration of 10%. Using the oily APMsuspension, APM-containing feed pellets were made by the same immersionprocedures as described in Example 1. The weight increase of feedpellets as measured after the immersion in the oily APM suspensionindicated that the amount of APM taken into the pellets was 5,000 ppm bymass. APM was extracted from the feed pellets and its amount wasmeasured. The measured value was 4,900 ppm by mass.

The APM-containing feed pellets were stored at 40° C. and, when one day,3 days, 5 days and 10 days elapsed, APM was extracted and its amount wasmeasured. The thus-measured retention (%) of APM content was 98%, 96%,95% and 95% when one day, 3 days, 5 days and 10 days elapsed,respectively.

Comparative Example 1

Solid feed pellets were made by the same procedures as described inExample 1 except that calcium salt of L-ascorbic acid (hereinafterabbreviated to “ASC”) was used instead of APM. ASC used was prepared bypulverizing the reagent available from Wako Pure Chemical Industries,Ltd., into an average particle diameter of 15 μm.

The ASC-containing feed pellets were tested for their ASC content. TheASC content was 220 ppm by mass. These feed pellets were further testedfor their ASC-content retention (%) by the same methods as described inExample 1. The results are shown in Table 4. TABLE 4 Retention of ASCcontent Number of days elapsed 1 3 5 10 Content of ASC (ppm) 180 110 6611 ASC Retention (%) 82 50 30 5

Comparative example 2

Solid feed pellets were made by the same procedures as described inExample 1 except that the same APM as used in Example 1 was initiallymixed together with fish meal, wheat flour, soybean cake meal and fishoil. The amount of APM added was 250 ppm by mass. The feed materialmixture was kneaded, extruded and then dried at 120° C. for 3 hours togive the solid feed pellets.

APM was extracted from the feed pellets and its content was measured.The measured content was 90 ppm by mass. Thus only 36% of the initiallyadded APM remained.

Example 7

By the same procedures as described in Example 1, solid feed pelletswere made except that magnesium salt of L-ascorbate 2-phosphate havingan average particle diameter of 500 μm was used instead of APM having anaverage particle diameter of 15 μm with all other conditions remainingthe same. The suspension of particles of magnesium salt of L-ascorbate2-phosphate in fish oil was not uniform, and deposition of thesuspension on the solid feed pellets was not uniform.

Industrial Applicability

The fish-farming solid feed of the present invention contains stabilizedvitamin C at a high proportion or high concentration in the surfacelayer portion thereof. The vitamin C contained in the solid feed isstable and exhibits high vitamin C titer which is reduced only to aminimum extent during the course of production and storage. Especiallyeven when the stabilized vitamin C-incorporated fish-farming solid feedhas a large size, or has incorporated therein a large amount ofvegetable oil and/or animal oil, the fish-farming solid feed exhibits ahigh vitamin C titer which is reduced only to a minor extent during thecourse of production and storage.

The fish-farming solid feed can be produced by a process wherein a fishfarming feed material is kneaded and shaped into a shaped product; theshaped product is dried; and then, the dried shaped product is contactedwith stabilized vitamin C having been dissolved, emulsified or dispersedin a liquid. When the dried shaped product is contacted with stabilizedvitamin C having been dispersed in vegetable oil and/or animal oil,especially in fish oil, the stability of vitamin C in the solid feed isremarkably enhanced.

The fish-farming solid feed is especially suitable for typical culturedfishes and crustaceans such as rainbow trout, red salmon, chum salmon,ayu sweet fish, Biwa trout, cherry salmon, tuna, white trevally, greateramberjack, Japanese amberjack, sea bream, Japanese seabass, tiger pufferand other puffer, bastard halibut, goldfish, common carp, Japanese eel,kuruma prawn and black tiger prawn.

1. A fish-farming solid feed containing stabilized vitamin C,characterized in that at least 50% by mass of stabilized vitamin C,based on the total weight thereof contained in the solid feed, ispresent in a surface layer portion of the solid feed, spanning from thesurface to a 1 mm depth.
 2. A fish-farming solid feed containingstabilized vitamin C, characterized in that the content of stabilizedvitamin C in a surface layer portion spanning from the surface to a 1 mmdepth of the solid feed is at least 50 ppm by mass.
 3. The fish-farmingsolid feed according to claim 1 or 2, wherein the content of stabilizedvitamin C in a surface layer portion spanning from the surface to a 1 mmdepth of the solid feed is at least 100 ppm by mass.
 4. The fish-farmingsolid feed according to claim 1 or 2, wherein the total content ofstabilized vitamin C in the solid feed is in the range of 25 ppm to5,000 ppm by mass.
 5. The fish-farming solid feed according to claim 1or 2, which further contains at least one kind of oil selected from thegroup consisting of vegetable oils and animal oils.
 6. The fish-farmingsolid feed according to claim 1 or 2, which further contains 10% to 40%by mass, based on the mass of the solid feed, of a fish oil.
 7. Thefish-farming solid feed according to claim 1 or 2, wherein the solidfeed has a water content of not larger than 10% by mass.
 8. Thefish-farming solid feed according to claim 1 or 2, which has a columnaror globular shape and has a diameter of at least 11 mm.
 9. Thefish-farming solid feed according to claim 1 or 2, wherein thestabilized vitamin C is a salt of L-ascorbate 2-phosphate.
 10. Thefish-farming solid feed according to claim 9, wherein the salt ofL-ascorbate 2-phosphate is at least one salt selected from the groupconsisting of magnesium, calcium, sodium and potassium salts ofL-ascorbate 2-phosphate, and mixed metal salts thereof.
 11. Thefish-farming solid feed according to claim 1 or 2, which is used forfeeding a fish or other aquatic animal selected from rainbow trout(Oncorhynchus mykiss), red salmon (sockeye salmon, Oncorhynchus nerka),chum salmon (keta salmon, Oncorhynchus keta), ayu sweet fish(plecoglossus altivelis), Biwa trout, cherry salmon (masu salmon,plecoglossus masou), tuna (Thunnini), white trevally (Pseudocaranxdentex), greater amberjack (Seriola dumerili), Japanese amberjack(Seriola quinqueradiata), sea bream (porgy, Sparidac), Japanese seabass(Lateolabrax japonicus), tiger puffer (ocellate puffer, Takifugurubripes), puffer (Teraodontidac), bastard halibut (paralichthysolivaceus), goldfish, common carp (Cyprinus carpio), Japanese eel(Anguilla japonica), kuruma prawn (Japanese shrimp, Penaeus japonicus)and black tiger prawn (giant tiger prawn, Penaeus monodon).
 12. Aprocess for producing a fish-farming solid feed as described in claim 1or 2, characterized in that a fish farming feed material is kneaded andshaped into a shaped product; the shaped product is dried; and then, thedried shaped product is contacted with stabilized vitamin C having beendissolved, emulsified or dispersed in a liquid.
 13. The process forproducing a fish-farming solid according to claim 12, wherein thekneading of the fish-farming feed material is carried out by a heatedkneader.
 14. The process for producing a fish-farming solid feedaccording to claim 12, wherein the drying of the shaped product iscarried out to an extent such that the water content in the shapedproduct is reduced to 10% by mass or lower.
 15. The process forproducing a fish-farming solid feed according to claim 12, wherein thedrying of the shaped product is carried out at a temperature of at least110° C.
 16. The process for producing a fish-farming solid feedaccording to claim 12, wherein the drying of the shaped product iscarried out for at least two hours.
 17. The process for producing afish-farming solid feed according to claim 12, wherein the stabilizedvitamin C is particles having an average particle diameter in the rangeof 5 μm to 300 μm.
 18. The process for producing a fish-farming solidfeed according to claim 12, wherein the liquid in which stabilizedvitamin C has been dispersed comprises at least one kind of oil selectedfrom the group consisting of vegetable oils and animal oils.
 19. Theprocess for producing a fish-farming solid feed according to claim 12,wherein the liquid in which stabilized vitamin C has been dispersedcomprises a fish oil.
 20. The process for producing a fish-farming solidfeed according to claim 12, wherein, after the dried shaped product iscontacted with stabilized vitamin C having been dissolved, emulsified ordispersed in the liquid, the resulting shaped product having the liquiddeposited thereon is dried.
 21. The process for producing a fish-farmingsolid feed according to claim 20, wherein the drying of the producthaving the liquid deposited thereon is carried out at a temperature ofnot higher than 90° C.
 22. The process for producing a fish-farmingsolid feed according to claim 12, wherein the as-produced fish-farmingsolid feed contains, as measured immediately after the productionthereof, at least 60% by mass of stabilized vitamin C based on theamount of stabilized vitamin C incorporated in the shaped product whenthe shaped product is contacted with the stabilized vitamin C-containingliquid.